The small mode areas for light propagating through optical fibers lead to high optical intensities even for moderate power levels. It is therefore no surprise that particularly a fiber input end, into which a laser beam is launched, can easily be destroyed, particularly when the fiber end is not very clean. The more surprising effect, however, is that a fiber can also burn down starting from the output end. Here, a bright white spot can be seen, which results from a hot plasma forming at the fiber end. As this plasma fuses the fiber, it propagates back towards the input end with a velocity which can be several meters per second. In standard single-mode fibers, this phenomenon can occur already for powers below 1 W if something (e.g. a burning dust particle) triggers the plasma at the output end. An important ingredient for the underlying mechanism is that the absorption losses of silica sharply rise at temperatures above 1000 °C.
The effect of fiber fuse can be disastrous in a telecom system where kilometers of fiber may be destroyed as a result of a failure at only one point. This is a concern for fiber-optic links with extremely high transmission capacities. A partial remedy may be to reduce the cladding diameter at certain points so that the fiber fuse is stopped at such locations .
Note that high-power fiber amplifiers are at particularly high risk of suffering fiber fuse; appropriate measures have to be taken to ensure device reliability.
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|||R. Kashyap, “The fiber fuse – from a curious effect to a critical issue: a 25th year retrospective”, Opt. Express 21 (5), 6422 (2013), DOI:10.1364/OE.21.006422|
|||S. Jiang et al., “Observation of fiber fuse propagation speed with high temporal resolution using heterodyne detection and time–frequency analysis”, Opt. Lett. 42 (17), 3355 (2017), DOI:10.1364/OL.42.003355|
|||S. Xiang et al., “Fiber fuse in chalcogenide photonic crystal fibers”, Opt. Lett. 43 (7), 1443 (2018), DOI:10.1364/OL.43.001443|
|||Q. Xiao et al., “Exploring the initiation of fiber fuse”, Scientific Reports 9, 11655 (2019)|
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